7166

• UCREFRP Catalog Number: 7166
• Author: Miller, W. H., et al.
• Title: Yampa River Fishes Study
• USFW Year: 1982.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

Colorado squawfish
Distribution and'Abundance - When all collections were combined, a total
of 87 adult Colorado squawfish (TLy 400 mm), including 11 recaptures,
was collected in 1981 from the Yampa and Green rivers. No juvenile
squawfish were collected. Seven YOY individuals (50 - 60 mm) were
collected from a backwater at Echo Park on the Green River, RM 344.5 (km
551.2), in September during the larval/YOY special investigations.
These data were strongly biased since different sampling programs (e.g.
efforts in some strata to capture large adults for radiotracking) resulted
in unequal sampling effort between strata. Only results from the standardized
sampling program can be used to obtain relative abundance data (Figure
10 and Table 14). Adults were captured in all strata except in the
Little Snake River and Stratum 3 on the Yampa. Electrofishing and
trammel net catch rates by strata of adult Colorado squawfish (Table 14)
were in agreement with total numbers captured (Figure 10). Highest
catch rates per hour were in Stratum 1 on the Green River (0.55 f ish/h)
and Stratum 4, 5, and 8 on the Yampa (0.51 fish/h, 0.36 f ish/h, and 0.39
fish/h, respectively).
Including all collections, the distribution of Colorado squawfish
by size classes (Table 15) showed no consistent pattern between strata
nor correlation with PHABSIM habitat weighted useable area (WUA) analyses.
The only individuals greater than 700 mm TL were found in Stratum 1 on
the Yampa. Twenty three percent (20 of 87) of the individuals captured
were between 600-700 mm. This high percent of large fish contrasts
markedly with percent of this size class in the White and lower Green
rivers (only 8% and .001%, respectively of total adults) (Harper and
Tyus 1982, Tyus et al. 1981). Of the 40 individuals (including recap-
tures) found in the lower Yampa Canyon (Stratum 1) 36 were collected
between 1 July and 10 July during special spawning and radiotracking
investigations (to be discussed later). Except for this brief period of
highly localized abundance, Colorado squawfish were rare in all collections.
Habitat Preferences - Habitat preferences of Colorado squawfish were
recorded by two different methods: 1) measurement of habitat parameters
at the point of collection, and 2) measurement of habitat parameters of
relocated radiotagged fish. Unfortunately, radiotracking data were not
available by the report deadline and a separate report on radiotracking
will be completed by FWS by mid 1982. Adult squawfish did not appear to
demonstrate narrow habitat requirements nor did the physical conditions
modeled in the PHABSIM procedures correlate with squawfish distribution
or prevalence (Appendix A).
Habitat and substrate types recorded at the point of capture for
adult Colorado squawfish, (Table 16) indicated a preference for runs
(31%), pools (26%), and shorelines (23%). Individuals were most often
captured over rubble (42%), sand (27%), and silt (18%) substrate. These
data are strongly influenced by the large number of spawning-condition
adults collected in restricted pool/riffle habitat over rubble bottom in
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